Medical treatment often requires the administration of a therapeutic agent (e.g., medicament, drugs, etc.) to a particular part of a patient's body. Intravenous injection has long been a mainstay in medical practice to deliver drugs systemically. Some maladies, however, require administration of drugs to anatomical regions to which access is more difficult to achieve.
A patient's eye is a prime example of a difficult-to-reach anatomical region. Ocular pathologies, such as diabetic retinopathy and macular degeneration, are typically treated by administration of drugs to the vitreous humor, which has no fluid communication with the vasculature. Such administration not only delivers the drug directly to where it is needed, but also minimizes the exposure of the rest of the patient's body to the drug and, therefore, to its potential side effects.
Injection of drug into the patient's body (e.g., into the vitreous humor of the eye), while medically feasible, typically delivers a bolus of the drug. Bolus injections may, however, present several problems. First, their use in treating chronic eye conditions typically necessitates repeated injections into the eye, a painful procedure that generally requires repeated and expensive visits to a physician's office, and can cause trauma to the eye. Second, because a bolus injection intrinsically produces a sawtooth-profile dependence of drug concentration over time, the dosage of the injection tends to be near the threshold limit of toxicity. Injection of such dosages typically increases the likelihood of systemic side effects, as occurs, for example, with ranibizumab.
A need therefore exists for apparatus and methods of administering appropriately chosen therapeutic drugs to the eye so that the time variation of the concentrations of those drugs in the eye is minimized.